1. Field of the Invention
The invention is directed to a method of controlling a motor of a power tool such as, in particular, a hand-held circular saw, and a control device for carrying out the method. The motor drives a disk-shaped tool of the power tool in an “on” position of a motor switch. For this purpose, a motor voltage in the amount of a nominal value is applied to the motor. The nominal value can be substantially fixed or can depend on a battery voltage or line voltage supplying the power tool. In each instance, an actual motor current applied to the motor is determined and compared to a first predetermined threshold in a first step. When it has been detected that an overload condition is met, a control process for protecting the motor from overloading is triggered automatically in a second step.
2. Description of the Prior Art
Control methods of the type mentioned above serve to protect the power tools in question against overloading of the motor. This overloading occurs, for example, when the disk-shaped tool is moved too quickly or with excessive pressing force relative to the material to be machined. Because of the increased resistance torque, this causes the motor to heat up which can lead to the destruction of the motor after a certain period of time.
Japanese Publication JP 4348809 discloses a stationary machine saw with a disk-shaped tool for cutting coilable material which automatically generates a movement of the tool relative to the coilable material during operation. A motor for driving the tool is protected against overloading by monitoring a motor current applied to the motor. As soon as this motor current exceeds a predetermined threshold, the forward feed movement of the tool relative to the material is reduced. Destructive heating of the motor can be prevented by means of this known control method.
However, this known procedure is based on a controlled movement of the tool relative to the material to be machined and is therefore not suited to hand-held power tools such as circular saws.